The PTB-920 is a 2-sided test bed for use with the PRF-911 Concentric Ring Fixture. The upper acrylic insulated surface is employed during surface resistance measurements in accordance with ANSI/ESD STM11.11.

The lower metal surface is equipped with a standard banana receptacle and is employed when making volume resistivity measurements as generally described in ANSI/ESD STM11.12. The metal side includes a standard banana receptacle for connection with the voltage lead.